Agression probably isn't the right word for it.

Defensive is probably better.

Baby ball pythons are programmed to be defensive - you are probably a potential predator from their view.

Did you allow a full week of time for the snake to be in the enclosure and get used to its surroundings with no handling or other unnecessary interaction?

Babies usually grow out of this. After you give your snake a week or more or settle in on their own, follow that with brief handling sessions a few times a week. Don't be afraid of the bites either...they are really not bad at all. They might draw a little bit of blood, once you wash it off, it's like nothing happened. My blood python nailed me this weekend and let me tell you...balls have NOTHING on blood pythons as far as bites go....

You want to build trust, while also letting them know that defensive displays don't scare you off. Otherwise, it just reinforces that behavior.

Hope this helps.